In search of experimental evidence for the biogeobattery

Recent work has suggested that the electrical self-potential (SP) geophysical technique may be used to noninvasively map redox conditions associated with contaminant plumes or bioremediation schemes. The proposed mechanism linking SP response and redox involves the generation of a current source and sink in the subsurface whereby electrons are transferred between anoxic and oxic environments via a conductive biofilm and/or biominerals, creating a biogeobattery. To investigate the conditions required for biogeobattery formation, we successfully created contrasting redox zones in a flow-through column setup. In this setup, an oxic section, containing clean sand, transitioned into an Fe(III)-reducing section. Fe(III) reduction was mediated by either a natural microbial community or a pure culture of the model organism Shewanella oneidensis MR-1 in two different column experiments. Visual observations and electron microscopy showed that ferrihydrite was sequentially transformed to goethite and magnetite; despite this change, no SP signal was generated in either column. Electron microscopy suggested that in the pure culture column, S. oneidensis MR-1 cells did not form a continuous, interconnected biofilm but rather interacted with the iron (oxyhydr)oxide surfaces as individual cells. In our experiments we therefore did not form the conductor of the biogeobattery. We thus conclude that generation of a biogeobattery is nontrivial and requires specific geochemical and microbiological conditions that will not occur at every contaminated site undergoing microbially mediated redox processes. This conclusion suggests that SP cannot be used in isolation to monitor subsurface biogeochemical conditions. Copyright 2011 by the American Geophysical Union.